The application of electrical principles in the repair of modern vehicles has become increasingly important for vehicle technicians as the electrical and electronic complexity of vehicles has increased. As hydrocarbons become scarcer and more expensive, the increased use of sophisticated electrical and electronic systems in vehicles to improve efficiency and economy will continue into the future. This trend is supported by the increasing popularity of hybrid vehicles and the investment by manufacturers in future technology, such as electric vehicles and fuel cell technology. To work on the current and future vehicles, it is increasingly important for the technician to have a sound understanding of electrical terminology, the behavior of electricity, and electrical component and circuit theory. The technician also needs to be able to read wiring diagrams, measure electrical quantities in the shop, calculate electrical values, and understand the quantities used. Your success as a technician will depend on your ability to apply these electrical principles and understand how they relate to the operation of virtually every vehicle system.

You are the Automotive Technician
The customer has complained that the fog lights no longer illuminate when turned on. Checking for a blown fuse is one of the first steps in diagnosing an electrical problem on any system in a car. The fuse box on the vehicle you are working on today is located on the passenger’s side cabin. The inside cover of the fuse box identifies the location of the fog light fuse. You test it with a DVOM and find battery power on only one side of the fuse, which indicates that it is blown. You then disconnect the wiring harness connectors from both fog lights and measure the resistance at the harness connector, between the input wire and the frame of the vehicle. The ohmmeter reads 0.2 ohms indicating a short circuit to ground. You see that the vehicle has had a winch installed recently. As you visually inspect the area, you see a bundle of wires pinched between the winch bracket and the vehicle’s frame. Loosening the winch bracket and removing the wires causes the ohmmeter to read an expected OL. To permanently solve the problem you will need to perform wire repairs on each of the damaged wires.
  1. What caused the fuse to blow?
  2. What other types of circuit protection devices do manufacturers use?
  3. What is the process for repairing wires in a harness?